Effect of Glyphosate on Aromatic Amino Acid Metabolism in Purple Nutsedge (Cyperus rotundus)¹

Abstract

The effect of glyphosate on aromatic amino acid metabolism in purple nutsedge sprouted tubers and shoots was investigated. Glyphosate at 33.5 mM caused inhibition of bud elongation, increased total free amino acid concentration, and caused rapid accumulation of shikimic acid in sprouted tubers. However, only one aromatic amino acid, tryptophan, decreased quickly to 22% of control 3 d after treatment (DAT) and remained low afterwards. This suggests that the inhibition of bud elongation is due to the rapid accumulation of shikimic acid and the repression of tryptophan synthesis. Foliar application of glyphosate at 14.5 mM to purple nutsedge shoots resulted in the rapid accumulation of glyphosate which was rapidly converted to its metabolite, aminomethylphosphoric acid. Free amino acids in leaves were also increased by glyphosate 3 DAT. The reduction in soluble protein 5 DAT and increased acid protease activity 3 DAT suggests that the late accumulation of free amino acids partially resulted from protein hydrolysis. Shikimic acid accumulated in glyphosate-treated leaves 5 DAT, but the concentration of the three aromatic amino acids was not reduced. This suggests that glyphosate toxicity in purple nutsedge shoots was associated with the rapid accumulation of glyphosate, followed by large accumulation of shikimic acid. Aromatic amino acids deficiency was apparently not a factor in toxicity.

Alterações no metabolismo da cana-de-açúcar em função da aplicação de maturadores

“…Matallo et al (2009), trabalhando com glyphosate e concentração de ácido chiquímico em citros, observaram que as plantas que receberam aplicação de glyphosate mostraram sempre maiores concentrações de ácido chiquímico que as plantas testemunhas. Vá-rios pesquisadores (Singh & Shaner, 1998;Wang, 2001;Mueller et al, 2003) (Mueller et al, 2003;Koger et al, 2005), algodão (Pline et al, 2002), girassol, trigo e milheto (Henry et al, 2007), soja (Singh & Shaner 1998) e trigo (Bresnahan et al, 2003.…”

“…Nesse contexto, o ácido chiquímico tem demonstrado ser um marcador seletivo para plantas expostas a subdoses de glyphosate (Harring et al, 1998;Singh & Shaner, 1998;Wang, 2001;Mueller et al, 2003).…”

Expression Profiles of <i>psbA, ALS, EPSPS</i>, and Other Chloroplastic Genes in Response to PSII-, ALS-, and EPSPS-Inhibitor Treatments in <i>Kochia scoparia</i>

“…Although both inhibit different pathways, glyphosate induces physiological responses similar to ALS-inhibitors in plants, resulting in an increased free amino acid content (as discussed above) and an impaired carbon metabolism leading to plant death [39] [42] [46]. Similar to ALS-inhibitors, glyphosate application also increases EPSPS transcript levels (Figure 3), possibly resulting in higher protein turnover and degradation.…”

Glyphosate as a tool to produce shikimic acid in plants

“…Koger et al, 2005a), to distinguish resistant from susceptible soybean and cotton cultivars (Pline et al, 2002;Bonini et al, 2009), and to check its effect on the metabolism of aromatic amino acids in Cyperus rotundus (Wang, 2001). Transitory in nature, shikimic acid accumulation has been reported to occur one day after glyphosate application, reaching peak levels between four and seven days afterwards (Koger et al, 2005b).…”